The invention relates to arrangements and methods for recovering unused energy from the exhaust gas of an internal combustion engine.
Internal combustion engines such as, for example, spark-ignition and diesel engines often have charging for reasons of power-to-weight ratio and efficiency. Here, so-called turbochargers or exhaust-gas turbochargers are widely used. In these, exhaust gas of the engine is conducted into the turbocharger to its turbine, which drives a turbocharger-compressor wheel. The turbocharger-compressor wheel compresses the intake air for the engine to an optimum value and conducts said intake air to the engine via the inlet valve either as air or else as a fuel/air mixture.
The exhaust-gas turbocharger and the associated internal combustion engine must be adapted to one another with regard to the characteristic curves for the delivery capacity of air and pressure of the compressed air. In particular during acceleration, when a large air quantity and a high pressure are required, an overdimensioned turbocharger is advantageous. On the other hand, an excessively high pressure and an excessively high delivery rate may be too high for example during steady-state operation of the engine and at the start of an overrun mode in a vehicle engine, as a result of which the efficiency of the turbocharger/internal combustion engine combination is reduced.
One solution for this situation is a turbocharger with a variable geometry, which is also referred to with the abbreviation VTG. Here, stationary guide wheels upstream of the exhaust-gas turbine are designed so as to be adjustable in order to provide adaptation to different conditions. A disadvantage here is that, in the steady-state situation, greater flow losses are generated by the adjusting mechanism with the result of a pressure drop, which can lead to an increased fuel consumption.
A further solution is a bypass valve which is also referred to as a wastegate. Said valve prevents the engine from being acted on with an excessively high charge pressure and prevents the turbocharger from accelerating into an excessively high rotational speed range. The wastegate is a valve which is arranged in the exhaust-gas flow upstream of the turbine and which opens under certain operating conditions and, in the form of a bypass, conducts a part of the exhaust gas directly into the exhaust pipe while bypassing the exhaust-gas turbine. The problems for the engine and turbocharger with regard to overloading are thereby solved. However, the disadvantage of a not inconsiderable energy loss, and therefore a reduced efficiency of the internal combustion engine, remains.
It is also known to extract air from the engine on the charge-air side of the turbocharger between the outlet of the turbocharger-compressor turbine and the inlet of the engine in certain operating states. This may take place for example by means of a charged air compressor, such as for example for a compressor for providing compressed air for a service brake. Here, however, an air quantity of the compressed air is branched off from the charge-air circuit of the engine, which may have an excessively low delivery capacity and is not adapted to the operating states of the engine and the turbocharger.
It is therefore an object of the present invention to create an arrangement for recovering the energy of exhaust gas of an internal combustion engine which no longer has the disadvantages specified above and which offers a higher efficiency in terms of fuel utilization.
The basic concept of the invention is adjustment of the quantity of the compressed intake air of a turbocharger device that can be extracted by an air compressor.
In this way, a wastegate valve can be considerably reduced in size or dispensed with entirely. The energy which escapes together with the exhaust gas through the wastegate valve, which energy was previously present in the unburned fuel, is recovered to a large extent and may be stored in a suitable way, as a result of which said energy can be accessed to a certain extent. Such accessing may increase the efficiency of the internal combustion engine by virtue of the stored energy being conducted back to the machine, for example in order to assist the engine in certain operating states, such as for example during starting.
Furthermore, an adjustable extraction of compressed intake air enables more precise setting of the turbocharger/engine combination, with the increased efficiency resulting in better economy.
In one preferred embodiment, it is provided that the partial quantity of the compressed intake air can be adjusted as a function of at least one operating parameter of the internal combustion engine and/or of at least one operating parameter of the turbocharger device. Here, it is possible to take the operating state both of the engine and also of the turbocharger into consideration in the extraction quantity of the partial quantity of compressed air, with it being possible in every operating state of the engine and of the turbocharger to obtain an optimum action of said combination. The operating states of the engine and of the turbocharger device are available in the form of parameters on the basis of measured values of sensors of already-existing engine controllers, such that no additional installations are required for this purpose.
In a further embodiment, it is provided that the partial quantity of the compressed intake air can be adjusted by a controllable extraction valve. For example, by an opening angle of a valve of said type, it is easily possible to adjust the partial quantity by simple electrical control impulses or voltages. Such valves are available commercially, cheaply and in high quality on the market.
In addition to or instead of said extraction valve, it is provided in an alternative embodiment that the extractable partial quantity of the compressed intake air can be adjusted by adjusting an intake quantity of the air compressor. For this purpose, use is made of a compressor with a relatively high power, which provides a higher compression pressure than present compressors. The air compressor is advantageously used for providing compressed air for a service brake. It may however also be an assembly, which is driven with assistance from the extracted air, in a vehicle, such as for example a fan for an air-conditioning system or the like.
If the air compressor is designed such that it can be driven in a controllable fashion in order to adjust the intake quantity, it is additionally possible to attain a finer gradation of the extracted partial quantity of the compressed intake air. This may take place by an electric drive of the air compressor and/or by a coupling to the internal combustion engine. Here, the coupling is for example advantageously switchable, as is the case with a clutch.
In an alternative embodiment, the air compressor may have at least one control valve for adjusting the intake quantity. The air compressor may for example be a radial compressor or piston compressor. Its valves may be designed as control valves and adjust the partial quantity of compressed air according to the operating state and requirement. The air compressor may however also have a plurality of compressor stages, cylinders or turbines which, depending on the requirement, may be activated or deactivated by control valves in order to extract the partial quantity of the compressed air of the turbocharger. It is also possible for this purpose to use the existing valves in a piston compressor, or said valves may be modified in a suitable way.
Since the air extracted from the air compressor is compressed and therefore has a certain energy quantity which was previously stored in the exhaust gas, said energy which is transmitted to the compressed air may also be used to assist the drive of the air compressor (or of the respective assembly).
It is also provided in one embodiment that the air compressor is connected to at least one air storage tank for storing the partial quantity of the compressed intake air. The partial quantity of compressed air extracted by the air compressor can be compressed further by the latter and conducted into a store, where it is for example added to the compressed air for a service brake. The partial quantity may however also be stored in a separate tank, from which it can then be accessed for different purposes (for example via certain valves and drive circuits for ventilation drive purposes or the like).
If the air compressor is of reversible design such that it can be driven by compressed air stored in the at least one air storage tank, the air compressor can operate as a motor and the exhaust-gas energy of the internal combustion engine stored in the air can be provided for assistance, such as for example during starting or in certain operating states such as driving on a flat surface.
For this purpose, the air compressor is coupled to the internal combustion engine, for example by means of a clutch. This coupling serves both for introducing a torque from the air compressor, which is driven by the stored air, into the internal combustion engine, and also for introducing a torque from the internal combustion engine into the air compressor in order to drive the latter in certain operating states.
In one embodiment, it is preferably provided that the arrangement has a control device for controlling the adjustable partial quantity of the compressed intake air. Said controller performs all the adjustments of operating parameters and characteristic maps of the internal combustion engine and of the motor which are stored for example in table form in memory devices. Said controller controls the respective valves and can then calculate, on the basis of the operating characteristic curve of the air compressor, what partial quantity of compressed air is/was extracted, and can provide said data to the superordinate engine control device, as a result of which the overall efficiency can be optimized. It is also possible here, taking into consideration the driver demand and the characteristic map of the engine and turbocharger, to calculate what exhaust-gas quantity will be produced during the next few charging cycles.
It is advantageous for the control device to be a constituent part of a control device of the internal combustion engine. This reduces the number of parts and the space requirement of components.
In an alternative embodiment, it is provided that the air compressor is designed as an intelligent air compressor with a separate control device. The latter may communicate with an existing engine controller for example via a bus within the vehicle. In the case in which the air compressor may form both an air motor and also a compressor, an intelligent compressor of said type is particularly advantageous. Here, it is for example possible for additional valves to be dispensed with, since these are already integrated in said air compressor. It is therefore merely necessary, for example, for the respective ports to be connected to the air tank and to the air line.
Here, it is also possible for the air compressor to be used, in one operating state, as an additional engine brake. For this purpose, the coupling to the internal combustion engine is activated, with for example the valves of the air compressor being closed, and said air compressor performing only compression work.
In a further alternative embodiment, the arrangement has an exhaust-gas compressor which is connected to an exhaust line of the internal combustion engine and which can be driven by the exhaust gas and which can be coupled to the internal combustion engine and/or is designed as an air compressor. Here, use is advantageously still made of energy of the exhaust gas in that the exhaust-gas compressor which is driven by the exhaust gas, as an air motor, generates a torque which, in order to assist the torque of the internal combustion engine, is conducted to the latter via a clutch. It is also possible for the compressor which is driven by the exhaust gas to operate as a further air compressor, compressing additional air and supplying said air to the air stores of the vehicle.
The exhaust-gas compressor can be controlled by means of at least one valve. It may also be designed as an intelligent compressor. It is of course also possible for the exhaust-gas compressor to be used as an additional engine brake by virtue of said exhaust-gas compressor being coupled to the internal combustion engine and performing compression work.
In yet a further embodiment, it is provided that the turbocharger device is connected to a secondary air supply device for the controlled supply of at least a partial quantity of compressed stored secondary air. It is thereby advantageously possible firstly to eliminate a so-called turbo lag and secondly to provide a further engine braking function. The engine braking function is obtained in that, in the engine braking state, the internal combustion engine compresses the supplied secondary air in addition to the intake air.
A further alternative design provides an arrangement for recovering energy from the exhaust gas of an internal combustion engine, which has the following:
a turbocharger device, which is driven by the exhaust gas, for generating compressed intake air for the internal combustion engine;
a first air motor which can be driven by stored compressed air and/or compressed intake air of the turbocharger device in order to generate a torque and which can be coupled to the internal combustion engine for a transmission of torque; and/or
a second air motor which can be driven by stored compressed air and/or exhaust gas of the internal combustion engine in order to generate a torque and which can be coupled to the internal combustion engine for a transmission of torque.
Here, it is preferable for the first air motor to be a reversible air compressor and for the second air motor to be a reversible exhaust-gas compressor. In each case two functions, specifically the compression of air and drive by means of air or exhaust gas, are therefore advantageously contained in one functional unit.
An internal combustion engine has the above-described arrangement for recovering energy from the exhaust gas of the internal combustion engine.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.